Inverse air injection technique



Dec. 15, 1959 J. c. TRANTHAM ETAL 2,917,112

INVERSE AIR INJECTION TECHNIQUE Filed Nov. 15, 1956 AiR OI L- BEARING FORMATION INVENTORS J.C. T RANTH AM A.R. SCHLEiCHER A TTORNEVS United States PatentO 2,917,112 INVERSE AIR INJECTION TECHNIQUE Joseph C. Trantham and Arthur R. Schleicher, Bartlesville, kla., assignors to Phillips Petroleum Company, a corporation of Delaware Application November 13, 1956, Serial No. 621,722

8 Claims. (Cl. 166-11) This invention relates to a process for the recovery or production of fluid hydrocarbons from underground formations containing hydrocarbon material by in situ combustion. A specific aspect of the invention is concerned with a method of initiating combustion in an in .situ combustion oil recovery process.

Recently impetus has been given to methods of recovering fluid hydrocarbons from underground formations containing the same by in situ combustion. Early attempts in this direction utilized direct air injection into a borehole in hydrocarbon-containing formations withheating of the formation so as to raise the same to ignition temperature. With viscous oils, this technique has not proved successful because of the building up of a heavy liquid bank of hydrocarbon material in the formation beyond the combustion front so that the flow of air thru the formation is cut off by the sealing of the formation. A recent technique, utilized with success, comprises initiating combustion around the initial borehole by heating up the formation and injecting air directly into the hot area so as to initiate combustion and establish a sulficient reservoir of heat in the formation to permit injection of air into the formation thru one or more offset boreholes so that air is forced thru the formation to the combustion area whereupon the burning is continued and the combustion front moves radially outwardly from the initial borehole and countercurrently to theflow of air. This technique, which is referred to as the inverse air injection technique, is fully disclosed in the copending application of John W. Marx, entitled Oil Recovery Process, Serial No. 526,388, filed August 4, 1955, now abandoned.

In establishing inverse air injection in the recovery of oil by inverse air injection combustion is initiated by direct air injection and it sometimes occurs that the flow of inverse air forces liquid hydrocarbon, built up in the formation during direct air injection, back into the combustion area whereby the combustion zone is cooled below combustion supporting temperature by the liquid oil. In such a situation the fire goes out and it is then necessary to again establish a combustion front.

Under some conditions of operation in establishing a combustion zone in an oil-bearing formation by direct air injection followed by inverse air injection, there is danger in producing an explosive mixture in the borehole and the surrounding formation thereby presenting an explosion hazard.

Accordingly, it is an object of the invention to provide an improved process or method of initiating, in situ, combustion in a gas-pervious underground formation containing carbonaceous deposits. Another object is to provide a method of initiating in situ combustion in an oil-bearing formation which lessens the possibility of explosion in the borehole thru which combustion is initiated. A further object is to provide a more effective method of initiating underground combustion when utilizing air injection and which avoids the difficulty of smothering when inverse air is forced into the combustion area. Other objects of the invention will become apparent from the accompanying disclosure.

The broadest aspect of the invention comprises heating up the carbonaceous-containing formation adjacent a borehole therein Where combustion is to be initiated without injecting hot gas, such as air, into the formation and then establishing combustion by passing inverse air to the heated zone from an area radially outside of the heated zone such as from an offset borehole in the formation within communicating distance of the initial borehole. The formation at the initial borehole is heated to combustion supporting temperature by any suitable means without forcing a substantial amount of gas into the formation thereby avoiding the building up of a heavy liquid bank in the formation radially outside of the heated area or in the fringes of the heated area. Heat is applied to the formation by means of an electric heater positioned in the borehole adjacent the oil bearing formation or by means of any other suitable device which heats up the formation without injection of substantial quantities of gas into the surrounding formation. A gas burner, such as a propane burner, has been utilized successfully as well as an electric heater. When utilizing a propane burner, the hot combustion products and flame contact the walls of the borehole so as to impart heat thereto and the combustion gas is vented from the borehole without passing into the formation in substantial amounts. The presence of combustion gas in the borehole excludes combustion supporting gas and reduces the explosion hazard when inverse air is passed thru the formation to the heated area. Other hot inert gas, such as nitrogen, CO and the like, may be passed in contact with the walls of the formation so as to heat up the same and then vented from the borehole. Utilizing this technique, the gases may be heated at the surface and injected into the borehole from a tubing extending to the oil-bearing formation or they may be heated in the area adjacent the formation by means of an electric heater or other suitable device.

In some formations, it is necessary to drive out water by pressurizing the formation from a borehole therein so as to drive the water to another borehole from which it is pumped by conventional means. After removal of the water, formation is heated around the combustion borehole and air is forced into the heated zone from one or more offset injection boreholes so as to establish a combustion front which then advances radially outwardly from the combustion borehole until the combustion front arrives at the injection boreholes.

In this embodiment of the invention, the injection of air is in progress from the surrounding formation while the area immediately adjacent the combustion borehole is being heated up so that air arrives at the heated area at approximately the time the formation is heated to combustion supporting temperature. In another embodiment Patented Dem-15, 1959.

of the invention, the inverse air is caused to flow thru the formation to the combustion borehole and heating is applied while the air is flowing from the formation into the borehole in which the heating takes place. in this technique, as soon as the wall of the borehole reaches ignition temperature and the concentration of oxygen in the gas passing into the borehole from the formation be comes combustion-supporting, burning commences and the combustion front begins to move radially outwardly from the borehole and the process is fully established.

A more complete understanding of the invention may be obtained by reference to the accompanying drawing which is a schematic view, partly in section, of an oil field showing apparatus suitable foreflecting the method of the invention.

Referring to the drawing, a combustion borehole 10 and an offset borehole 12 penetrate an oil bearing formation 14 at spaced-apart locations which permit the forcing of air from one well bore to the other. A casing 16 and a tubing 18 are positioned in borehole It}. Line 29 connects with casing 16 and provides an independent outlet therefrom. Casing 22 and tubing 24 are inserted in well bore 12. Lines 25 and 27 provide for introduction and/or withdrawal of fluids from their respective tubing. A suitable heater 26 is positioned in tubing 18 opposite formation 14 to provide a means for heating up a zone 28 information 14 to combustion-supporting temperature. When heater 26 comprises a gas burner the combustion gasis vented thru lines 25 or 27. When an electric heater is utilized for heating up the formation it is usually desirable to displace the gas in the well bore adjacent the formation with an inert gas which does not support combustion.

Formation 14 is heated to ignition temperature in area 28 by suitable means and air or other free-oXygen-containing gas is injected into borehole 12, preferably thru tubing 24, under pressure so as to force the air thru the formation to the heated area 28 and thereby establish combustion upon arrival in the heated area in combustion-supporting concentration. Combustion products and fluid hydrocarbons swept from the formation by the combustion process and flow of gases are recovered from borehole 10 thru tubing 18. Continued inverse air injection moves the combustion front toward the input well 12 so as to produce a substantial amount of hydrocarbon from the intervening formation. Inverse injection of air in a or 7 hole pattern around borehole it) produces oil from the area completely surrounding the combustion borehole. Of course, any number of wells or bore holes 12 may be utilized as injection boreholes but the number will be limited by the economics of the situation. It is also feasible to utilize borehole as an injection borehole and a plurality of surrounding boreholes as combustion boreholes so that the combustion zone moves inwardly toward borehole 10. In this manner surrounding boreholes become production boreholes.

Recovery of oil by inverse air injection, as outlined herein, produces a substantial proportion of the hydrocarbon in the formation but also leaves in the formation a substantial amount of residual hydrocarbon in the form of coke and possibly some re-condensed liquid hydrocarbon. Continued injection of air after the combustion front arrives at the injection borehole or boreholes causes the combustion front to reverse and travel back to the borehole in which combustion was initiated, thus driving .4 of the tube. The container was filled with nitrogen and the heater was turned on so as to raise the temperature at the end of the tube adjacent the heater to 420 F. over a period of five minutes. At this time air was passed into the opposite end of the packed tube at the rate of 300 standard cubic feet per hour per square foot of cross section. After 30 minutes the temperature rose to 480 and during the succeeding 15 minutes the temperature rose to 620 F. and soon went to 1060 F. This clearly indicated that combustion of the oil in the packed sand was well established.

In the field test the oil sand lay in a layer from to 64 feet below the surface level. Two wells penetrated the formation in the manner shown in the drawing. Water was driven out by forcing air into well 10 until water was excluded from the circular region including well 12; then well 10 was pressured to 46 p.s.i.g. with nitrogen and well 12 was pressured with air to 45 p.s.i.g. After the water was driven from the formation, heater 26 was turned on and delivered energy at the rate of 8 kilowatts for 4 days and the temperature in the wellbore rose to the range of 900 to 1000 F. At this time, well 10 was opened to production and air was allowed to pass thru the formation from well 12 which was still under a pressure of 45 p.s.i.g., the heater remaining in operation. The temperature then began to rise and soon reached l4G0 F. at which time the heater was shut off in sections (parallel heating elements) in order to keep the emperature down below 1400" F. However, the temperature continued to rise and the heater was shut off entirely. Further rise in temperature in the combustion area. indicated that combustion had been established in the formation by inverse air injection. The CO content in the efliuent from well it} rose to the range of '10 to 15% providing further evidence that combustion was taking place. Other evidence of this Was found in the oxygen content of the effluent or production stream which went down to substantially zero. During the first stage of the burning, oil was recovered having a 20-25 API gravity.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. A process for initiating in situ combustion in a gas pervious underground carbonaceous formation around a borehole therein, said formation containing normally solid hydrocarbons, which comprises heating said formation adjacent said borehole to a temperature above the combustion temperature of the carbonaceous material; maintaining a noncombustible atmosphere in said borehole adjacent said formation during heating thereof so that substantial combustion of said formation hydrocarbons is prevented, and while at said temperature, passing freeoxygen-containing gas to the hot carbonaceous material thru the formation from an area spaced radially outside of said borehole so as to ignite and initiate in situ combustion of said material, whereby accumulation of a heavy viscous liquid bank in the formation in advance of the resultant combustion front is avoided.

2. The process of claim 1 including circulating freeoxygen-containing gas from said spaced radial area to said borehole while heating said formation to initiate combustion therein when the ignition temperature is reached.

3. A process for recovering hydrocarbons from a gaspervious underground formation containing heavy viscous oil which comprises heating said formation adjacent an ignition borehole therein to a combustion-supporting temperature; maintaining a non-combustible atmosphere in said ignition borehole adjacent said formation during said heating so that substantial combustion of formation hydrocarbon is prevented; while the heated formation is at said temperature, passing air thereto by injecting same into said formation thru at least one oifset borehole therein so as to ignite and initiate in situ combustion in said formation; avoiding injection of gas into said formation from said ignition borehole during the heating and ignition steps, whereby accumulation of a heavy viscous liquid bank in the formation in advance of the resulting combustion front is avoided; and recovering hydrocarbons produced by the combustion from said ignition borehole.

4. The process of claim 3 wherein said non-combustible atmosphere comprises a non-oxidizing gas.

5. The process of claim 4 wherein said gas is heated to a temperature above combustion-supporting temperature so as to heat said formation.

6 6. The process of claim 4 wherein said gas comprises C0 7 7. The process of claim 4 wherein said gas comprises N 8. The process of claim 4 wherein said gas comprises combustion gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,107,416 Dunn Aug. 18, 1914 1,457,479 Wolcott June 5, 1923 1,494,735 Cooper May 20, 1924 2,497,868 Dalin Feb. 21, 1950 2,793,696 Morse May 28, 1957 

1. A PROCESS FOR INITIATING IN SITU COMBUSTION IN A GASPERVIOUS UNDERGROUND CARBONACEOUS FORMATION AROUND A BOREHOLE THEREIN, SAID FORMATION CONTAINING NORMALLY SOLID HYDROCARBONS, WHICH COMPRISES HEATING SAID FORMATION ADJACENT SAID BOREHOLE TO A TEMPERATUE ABOVE THE COMBUSTION TEMPERATURE OF THE CARBONACEOUS MATERIAL; MAINTAINING A NONCOMBUSTIBLE ATMOSPHERE IN SAID BOREHOLE ADJACENT SAID FORMATION DURING HEATING THEREOF SO THAT SUBSTANTIAL COMBUSTION OF SAID FORMATION HYDROCARBONS IS PREVENTED, AND WHILE AT SAID TEMPERATURE, PASSING FREEOXYGEN-CONTAINING GAS TO THE HOT CARBONACEOUS MATERIAL THRU THE FORMATION FROM AN AREA SPACED RADIALLY OUTSIDE 